There have been developed thermosensitive recording devices capable of charting high-quality pictures, equivalent to those of electrostatic plotter, at a high speed (10 to 25 mm/sec) as a substitute for a means for making drawing with electrostatic plotter of CAD or CAM. The thermosensitive recording devices are on sale at a price of about 1/2 of that of electrostatic plotter device.
Such raster scan method type thermosensitive recording device has an advantage in that operator can be liberated from blue printing work, since the same drawing can be continuously output on the level of the original drawing by utilizing repeat function. Accordingly, opaque thermosensitive recording paper can be used. As this kind of thermosensitive recording paper, there are conventionally used thermosensitive recording paper obtained by calendaring paper (Bekk index (JIS P-8119): 120 seconds or below) made of natural pulp to smooth it (Bekk index: 150-1,100 seconds), coating a thermosensitive recording layer thereon, drying it and calendaring the thermosensitive recording layer coated paper to smooth it. As this kind of thermosensitive recording paper, however, attempts are made to use opaque (opacity: 90 to 95%) synthetic paper from the viewpoints of the preservability of the original drawing and high-speed printability, said opaque synthetic paper being used as a support for thermosensitive recording image receiving paper [see, JP-A-63-22289l (the term "JP-A" as used herein means an "unexamined published Japanese patent application", JP-A-62-299391, JP-A-62-148292, JP-A-62-279983, JP-A-62-299390, JP-A-62-87390, JP-A-63-290790, JP-A-63-307988 and JP-A-63-315293].
Thermosensitive recording paper using semi-transparent synthetic paper has high Bekk smoothness (600 to 2500 seconds), is superior in high speed printability and has excellent preservability. However, it is demanded to make improvements in pencil writeability and erasability with erasers, because a degree of smoothness is too high. Further, it is demanded to develop semi-transparent thermosensitive recording paper which allows diazo copying to be made as in electrostatic plotting paper for CAD.